(a) Field of the Invention
The present invention relates to an antenna that comprises a helical antenna installed on an outer upper part of a portable wireless apparatus, and a rod antenna that passes through an inner part of the helical antenna and is extendable to the outside of the wireless apparatus and contractible inside of the wireless apparatus. More specifically, the present invention relates to an antenna in which a helical antenna transmits and receives radio frequency (RF) signals when a rod antenna is contracted, and the helical antenna can be separated from a feeding connector of the antenna apparatus and the rod antenna can become free from any coupling effects with the helical antenna and can transmit and receive RF signals when the rod antenna is extended.
(b) Description of the Related Art
Generally, the portable wireless apparatus adopts a fixable type helical antenna, an extendible and contractible antenna in which a helical antenna is fixed on an upper part of a rod antenna in one unit, or an extendible and contractible antenna in which a helical antenna is fixed on an outer upper part of a wireless apparatus with a rod antenna passing through an inner part of the helical antenna and extending and contracting from and into the wireless apparatus.
A fixable antenna conventionally comprises a helical antenna having wave length of .lambda./2 or .lambda./4. Since the physical length of the antenna is far shorter than 1.lambda., the helical antenna has drawbacks of a narrow bandwidth and low radiation efficiency.
To overcome the problems that the fixable antenna has and to provide for the portability of the wireless apparatus, the above-noted two extendible and contractible antennas have been developed and are widely used.
A European patent No. 0516490 discloses a contractible antenna in which a helical antenna is fixed on an upper part of a rod antenna as an integrated unit. When the rod antenna is contracted, the helical antenna is coupled to a feeding line of the wireless apparatus in order to operate, and when the rod antenna is extended, the rod antenna is coupled to the feeding line of the wireless apparatus while the helical antenna is disconnected from the feeding line. Since the center of gravity of the antenna becomes positioned at the helical antenna that is fixed on the upper part of the rod antenna in an integrated unit when the rod antenna is extended, if the user drops the wireless apparatus on the ground, a plastic joint which couples the helical antenna with the rod antenna c an b e easily broken.
The U.S. Pat. No. 4,868,576 discloses an extendible and contractible antenna comprises an antenna housing with a built-in helical antenna, being fixed on the outer upper part of the wireless apparatus; and a rod antenna which passes through the inner part of the helical antenna which is extended and contracted. When contracted, an insulated portion of the upper part of the rod antenna in the extendible and contractible antenna is positioned in the inner part of the helical antenna, and thereby, only the helical antenna works. When extended, the helical antenna and the rod antenna must be coupled in a capacitive manner while the helical antenna is coupled to the feeding line of the wireless apparatus. For this capacitive coupling, the helical antenna and the rod antenna have to be precisely matched.
U.S. Pat. Nos. 5,612,704 and 5,825,330 were disclosed to solve the above-noted problem. In the case of extension of the rod antenna, a portion of a lower part of the rod antenna contacts the helical antenna, and therefore, the helical antenna is electrically disconnected, which is referred to as the short circuit method. In order to achieve these electrical characteristics, the helical antenna must directly contact the rod antenna, and in this case, the helical antenna or rod antenna may be changed in its form. This may cause dangerous modification of the characteristics of the antenna and also requires high precision in the manufacture of the antennas.